The present exemplary embodiment relates to barrier diodes. It finds particular application in conjunction with Schottky diodes fabricated utilizing refractory metal borides and nickel gallide to interface with a silicon carbide semiconductor substrate. This device provides greater barrier height and performance at high temperatures, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
Silicon carbide (SiC) has material properties such as a wide band gap, a high thermal conductivity, a high electron saturation velocity, and a high breakdown field. These aspects have made it one of the most promising materials for many high-power and high-temperature electronic device applications. Consequently, a great deal of research effort has been put into the study of this material in the past twenty years, leading to the demonstration of new electronic device structures with remarkable performance. Application areas include wireless technologies for commercial and military needs, high efficiency switches for power distribution, harsh environment sensors, and uses in the automobile industry.
At the present time, one of the major limitations to the full performance of SiC-based devices is related to Schottky and ohmic metal contacts. In particular, Schottky contacts with high a Schottky barrier height (SBH) and a good thermal stability are essential for operations involving high temperature, high gain, and low power consumption. Selection of Schottky contact metals is generally guided by the reaction chemistry at the metal/semiconductor interface and by the Schottky-Mott theory, which predicts the energy barrier φb (barrier height) to the flow of electrons. For this reason, several high work function metals such as Pt, Ni, Au, and Pd have been investigated as Schottky contacts to n-type SiC. Although technological advancement has led to the commercial availability of SiC-based Schottky diodes, their performances still require further improvement especially to ensure reproducibility and reduced reverse bias currents of the devices.
Ni and Ti are the metals most widely used in the fabrication of SiC Schottky diodes. However, Ni/SiC Schottky diodes have been shown to produce non-ideal current-voltage (I-V) characteristics accompanied by dependence of SBH on the surface preparation conditions. Such contacts have been improved by sintering the Ni between 500° C. and 600° C. to form nickel silicide (N2Si). In the process of interfacial solid-state reaction, some SiC material is consumed. However, this process can be undesirable in submicrometer device structures, and Ni/SiC Schottky contacts change to ohmic contact when annealed at ˜800° C. for two minutes. The formation of silicides or carbides by several refractory metals (e.g., Co, Ni, Cr, Fe, Pt, Pd, and W), including the interdiffusion of other metals such as Pt and Au noted at temperatures as low as 450° C., is indicative of poor thermal stability, which could eventually lead to the degradation of the Schottky characteristics.
A Schottky barrier diode (SBD), unlike conventional PiN diodes, is a majority carrier device in which the absence of minority carrier storage effects leads to faster switching speeds. In addition, SBDs based on SiC materials have large blocking voltages and can function reliably at higher temperatures. These properties make SiC-based SBDs a primary choice for operations involving high power, high frequency and high temperature (600° C. and above). Although SiC-based SBDs are commercially available, they are rated for operation temperatures below 180° C.
What are needed are systems and methods to improve thermal reliability and electrical properties of Schottky diodes for high power and high temperature applications.